1. Field of the Invention
The subject invention generally pertains to electronic power conversion circuits, and more specifically to high frequency, switched mode electronic power converters. Some of the subject matter of this application was first revealed in Disclosure Document Number 527396.
2. Description of Related Art
Many electronic circuits require power at more than one voltage, so power supply manufacturers offer power supplies with multiple regulated outputs. This was often an application for magnetic amplifiers, but magnetic amplifiers have become less popular as switching frequencies have risen and silicon semiconductor prices have fallen. One common way of providing additional regulated outputs in current use is illustrated in FIG. 1. Operational wave forms for the FIG. 1 circuit are illustrated in FIG. 2. In FIG. 1 a second regulated output is provided by a synchronously switched buck post regulator, which is a sort of semiconductor magnetic amplifier. In the FIG. 1 circuit an output choke L1 is provided for the main output and a second output choke L2 is provided for the second output. In general the first output voltage is fed back to control the primary switch and the second output is regulated with a local feedback loop which controls the delay in the turn on time of MS2A with respect to the turn on time of MS1A. This is leading edge modulation which is similar to that used in a magnetic amplifier. In most of these power converters there is a maximum power level which is the sum of the powers of the two outputs, but either of the two outputs can be operated at or near the maximum power level. This requires two output chokes each of which must be sized for the converter's maximum power level. An alternate method is illustrated in FIG. 3. The FIG. 3 circuit uses a coupled output choke to obviate two separate magnetic circuit elements sized for maximum power. In the coupled inductor the single core must be sized for maximum power and the window area must be sized to accommodate two windings each of which must be capable of accommodating the maximum output power. This is an improvement which results in a smaller and cheaper output choke, compared to the FIG. 1 circuit. The disadvantage of the FIG. 3 circuit is that the second output is not independently regulated and two secondary windings are required on the main transformer. What is needed is a circuit that achieves the performance of the FIG. 1 circuit but with lower total output choke volume.